In a wireless communications system, each device needs to transmit information by using frequency resources. Frequency resources are also referred to as spectrums. Spectrums may be classified into licensed spectrums and unlicensed spectrums. The licensed spectrums are dedicated frequency resources of some operators, and the unlicensed spectrums are frequency resources for public use in a wireless communications network. With development of communications technologies, an amount of information transmitted in the wireless communications network increases on a daily basis, and a data throughput in the wireless communications network may be improved by preempting an unlicensed spectrum to transmit information, so as to better satisfy user requirements.
However, when a device preempts an unlicensed spectrum to perform data transmission, after the device successfully preempts a channel of the unlicensed spectrum, data may be sent at a random moment. Therefore, the device may not send data at a starting moment of a complete subframe, that is, the device may not send a complete subframe. In this case, data is encoded according to an original bit rate, and during sending, only a part of encoded data can be sent. Consequently, some encoded data still cannot be sent. In this way, to ensure correct decoding at a receive end, when retransmission is performed subsequently, a relatively low retransmission bit rate needs to be used, causing a waste of system resources.